Those guys are pretty scarry! I've never really used them myself (I prefer the Greek factions). All I know is that they tend to rip my armies appart when I don't expect them.

And I've tried throwing cavalry, infantry, pikes at them, skirmishers (not enough missiles)... The only thing that works for me is to pepper them with archers from far away for a long time - thank the gods for Cretan Archers! (they just won't die... scarry...)

So, my advice. Get them. At least two units. I would put them behind my front line and throw them into the line wherever my legions start to waver. They can absorb a massive amount of arrows too (ironically). Just keep in mind that they have a peasant-like formation.